The observation of focal brain swelling and brain herniations suggests that pressure gradients exist in the injured brain. Using the model of vasogenic edema induced by a cryogenic lesion in the cat, the time course of brain tissue pressure and brain water in specific brain sites will be quantitated. The relation of these pressures to intrabrain volume increases will be determined. Local CBF (H2 electrode) may or may not change in areas of increased tissue pressure and increased brain water but rather the control mechanisms of CBF may be altered so that tissue pressure fluctuations affect CBF and changes of CBF affect tissue pressure causing relentless and progressive expansion of the area of swollen brain.